To investigate the role of nuclear versus cytoplasmic signaling in the expression of cell cycle related genes in mammalian cells over expressing cyclin D1. (1) Does nuclear versus cytoplasmic alpha particle irradiation differentially arrest cell cycle progression and is this a function of the p53 status of the cells? (2) Does nuclear versus cytoplasmic irradiation differentially alter cellular levels of (I) the p53 protein (ii) cyclins D, E or A (iii) CDK's 2 or 4 (iv) the Rb protein or the extent of phospharylation of the Rb protein"